1. Field of Invention
The present invention relates to an emission device, surface light source device, display, and light flux control member used therein. The present invention is applied, for instance, to backlighting arrangements for liquid crystal display panel, various illumination devices for general uses such as interior illumination, or displays composed of illumination device and member to be irradiated.
2. Related Art
A surface light source device employing a plurality of LEDs (light emitting diodes) as point-like light sources has been known as an illuminating means for a LCD monitor display of a personal computer or TV set. A plate-like light flux control member having roughly the same shape as that of a LCD panel is employed in the surface light source device, being provided with a plurality of LEDs arranged like a matrix at the back side. The LEDs emit light which is incident to a back face of the light flux control member and travels within the light flux control member to an emission face opposite to the back face, being outputted from the emission face toward a LCD panel to be backlighted. Prior arts like this have been disclosed in the following documents.
<Prior Art 1>
This is found disclosed in Tokkai 2002-49326 (JP-A 2002-49326), according to which surface light source device 10 is provided with microlens array 102. Individual microlenses are arranged in one-to-one correspondence to a plurality of LEDs 101, as shown in FIG. 12. Light from LEDs 101 is outputted in a direction perpendicular to a plane (upward) via microlens array 102.
<Prior Art 2>
This is found disclosed in Tokkaisho 59-226381(JP-A 1984-226381), according to which emission display device 103 is provided with LED 104, concave lens 105 and convex lens 106, as shown in FIG. 13. Light from LED 104 is condensed by convex lens 106 after being diverged by concave lens 105, being outputted in a direction roughly parallel with an “optical axis” of LED 104. Please note that “optical axis” is defined as a light travelling direction at a center of three-dimensional light flux emitted from a point-like light source (LED 104).
<Prior Art 3>
This is found disclosed in Tokkaisho 63-6702 (JP-A 1988-6702), providing display 107 having LED(s) 108, as shown in FIG. 14. Light from LED 108 is condensed by condenser lens 110 and directed forward, then being diverged by diverging lens 111.
<Prior Art 4>
Another prior art provides display 121 as shown in FIG. 15. Display 121 is provided with a plurality of LED chips 125, light diffusion member 126 and member 127 (such as LCD panel) irradiated by light transmitted through light diffusion member 126. LED chips 125, each of which is composed of LED 124 and light flux control member 123 fixed on an emission surface side, are arranged at intervals, for instance, at regular intervals. Light flux control member 123 has hemisphere-like emission surface 122. Object 127 is supplied with light emitted from LED chips 125 and then transmitted through light diffusion member 126.
However, the above prior arts involve problems as follows.
(1) Prior Art 1;
Surface light source device 100 has a portion at which configuration of microlens array 102 varies discontinuously. The portion is located between LEDs 101 adjacent to each other. Emission intensity changes sharply at this discontinuity portion, with the result that a conspicuous unevenness in brightness appears around boundary regions between individual microlenses of microlens array 102.
(2) Prior Art 2;
It is difficult to say that concave lenses 105 in emission display 103 are coupled with each other continuously to form a plane. Further to this, convex lenses 106 are scarcely coupled with each other continuously to form a plane. Therefore, a member of a large area to be illuminated, such as large-screen liquid crystal display panel, is hardly supplied with uniform illumination light.
(3) Prior Art 3;
With display 107, light from LED 108 is diverged by diverging lens 111 after being condensed by condenser lens 110. This wil reduce unevenness in brightness as compared with Prior Art 1. However, a sufficient mixing of light fluxes from LEDs 108 adjacent to each other is hardly expected, with the result that unevenness in emission color between individual LEDs 108 tends to be conspicuous.
(4) Prior Art 4;
With display 121, wave-shaped brightness unevenness appears strikingly corresponding to LEDs 124 arranged at intervals, as shown in FIG. 10. This brings dark areas corresponding to absence of LED 124 between LED s 124, making uniform illumination difficult. In addition, Prior Art 4 tends to give a locally large brightness area in the vicinity of optical axis L of LED 125. Therefore, it is difficult to male light from LEDs 124 adjacent to each other mixed well, with the result that unevenness in emission color between individual LEDs 124 tends to be conspicuous.